💡 Today I Learned

Custom Errors in asp.net mvc 5

(note This is not for .net core)

  1. Inside system.web element in the web.config file:

     <customErrors defaultRedirect="~/Error" mode="On">
 	<error statusCode="404" redirect="~/Error/NotFound" />
 	<error statusCode="403" redirect="~/Error/Forbidden" />
 	<error statusCode="407" redirect="~/Error/Security" />
 </customErrors>

  2. In FilterConfig ensure you are not adding a HandleErrorAttribute

     public static void RegisterGlobalFilters(GlobalFilterCollection filters)
 {
 	//filters.Add(new HandleErrorAttribute()); //Ensure this is commented out or deleted.
 }

  3. Create an Error controller.

     public class ErrorController : Controller
 {
 	public ActionResult Index()
 	{
 		Response.TrySkipIisCustomErrors = true;
 		// This will load Views/Shared/Error.cshtml
 		return View("Error");
 	}

 	public ActionResult NotFound()
 	{
 		Response.StatusCode = 404;
 		Response.TrySkipIisCustomErrors = true;
 		// This will load Views/Error/View.cshtml
 		return View();
 	}

 	public ActionResult Forbidden()
 	{
 		Response.StatusCode = 403;
 		Response.TrySkipIisCustomErrors = true;
 		// This will load Views/Error/Forbidden.cshtml
 		return View();
 	}
 }

In an action where you look for a resource but can't find it... don't do this:

return this.HttpNotFound(); // don't do this! see below...

...as that will end up at the IIS error page, not your custom error page. instead do this:

throw new System.Web.HttpException(404, "No such project");

...and it will end up on your "NotFound" page.

Inside those error handling views, I have things like this:

@model System.Web.Mvc.HandleErrorInfo
@{
	ViewBag.Title = "Error";
}
<img src="/images/Doh.jpg" alt="Homer Simpson giving a Doh reaction" title="Missing" style="float:right;margin:30px;" />
<h1 class="error">404 - File not found.</h1>
@if (Model != null)
{
	<h2 class="error">@Model.Exception.Message</h2>
	if (Authorized.Admin() || Authorized.Editor())
	{
		<p>
			Exception of type: <code><strong>@Model.Exception.GetType().Name</strong></code><br />
			Thrown in <code>Controller: <strong>@Model.ControllerName</strong>, Action: <strong>@Model.ActionName</strong></code>
		</p>
		<h2>Details:</h2>
		<p>@Html.Raw(Model.Exception.ToString().Replace("\r\n", "<br />\r\n"))</p>
	}
}
else
{
	<h2 class="error">Look not here. We cannot find that which you seek.</h2>
}

The line if (Authorized.Admin() || Authorized.Editor()) is specific to my situation.

Others recommend:

@if(Model != null && HttpContext.Current.IsDebuggingEnabled)

Previously/Sources

Previously I wrote this nasty article which showed a way to get very confused by custom errors in asp.net mvc (including deliberate typos)

One comment there was very helpful, but a particular stack overflow answer was most helpful.

See also